1. Field
This disclosure relates generally to non-volatile memories (NVMs), and more specifically, to NVMs that include soft programming.
2. Related Art
Non-volatile memories (NVMs) generally require special operations for program and erase and there is a limit to how many times these operations can be performed. During an erase memory cells that have been erased successfully may continue to be subjected to erase conditions while other memory cells are still being erased. These bits that are slow to erase may be referenced as slow bits. Some memory cells may be over-erased that then must be subjected to compaction and then soft programmed to overcome the problems associated with over-erase such as excessive leakage as part of the embedded erase operation. Soft programming typically takes a relatively long time since it is done per address and with low bias. With more cells required to be soft programmed, it may eventually cause the embedded erase operation to fail to complete within the specified maximum time. Soft program time is the major part of the embedded erase time. For large blocks (>64 kB), soft program time dominates the embedded erase time. Another issue over time and perhaps tens of thousands of cycles or more is that memory cells become weak or slow to erase and so does the soft program. The long erase time can become a significant and may be only relevant to a few bits which are slow to erase, thus cause the main population to be over erased. Thus it requires even longer soft program time to finish embedded erase.
Accordingly, there is a need for an NVM system to improve upon one or more of the issues raised above.